When I first spotted Marco, a muscular, middle-aged man who came to the emergency department one recent Sunday morning, he was seated in a chair by the nurses’ station as his vital signs were being taken. He looked extremely healthy until he stood up and tried to walk in a pair of fluffy bedroom slippers he was wearing. It was obvious that every step he took caused severe pain.

Marco, I soon learned, ran a construction business. A few days earlier, he had gone to inspect a construction site clad in a sweatshirt, jeans and sneakers. That is when he stepped on a nail that protruded from a small piece of lumber. The nail punctured the bottom of his sneaker and went deep into the ball of his right foot.

Rather expectedly, his foot was sore that night. But because he had been given a tetanus shot earlier in the year, he assumed that he’d be fine. The following day, Marco’s right foot was swollen and tender, but he squeezed his foot into a construction boot and went about his business. Hour by hour, the foot became more painful. On Sunday morning, Marco could no longer bear the pain nor stand normally on his right foot.

When I examined Marco’s foot, it was extremely tender. The area was also very swollen and warm to touch. An X-ray showed that a tiny bone fragment had broken off within the foot, presumably caused by the nail. With all of Marco’s symptoms pointing toward an infection, I started him on broad-spectrum IV antibiotics. I then consulted the on-call orthopedist, who took Marco to the operating room that afternoon to “clean out” the infection, which had become quite serious. After two weeks of antibiotics, Marco recovered.

Like Marco, the majority of people who develop an infection after stepping on a nail, a screw or another sharp object while wearing sneakers contract “Sneaker Foot.” This type of infection is caused mainly by Pseudomonas bacteria, which are not usually found on a healthy person’s skin but are extremely common in the warm, moist and dark environment of an old sneaker. These bugs thrive on the materials used in sneaker soles.

That’s right—the infection comes from your shoe, not from whatever punctured your foot! Pseudomonas is extremely hard to treat with oral antibiotics alone. When the infection is as advanced as it was in this case, the patient often needs surgery to ensure a reasonable recovery. This germ can destroy a bone and even deform the foot.

Lesson learned: If you suffer a puncture wound to the foot—especially if you’re wearing a sneaker—and develop swelling, increasing pain and tenderness, redness or oozing, get to a hospital emergency department!

Although most people immediately think of tetanus (lockjaw) when this type of wound occurs, only about 29 cases of tetanus are reported in the US annually—most of them in people who never had or did not stay current with tetanus immunizations (the recommendation is every 10 years). However, as many as one in 10 patients who requires care for a significant puncture wound to the foot will develop a serious infection.